1. Field of the Invention
The present invention relates to a jog method for an optical disk player, for example, a laser disk player which uses an optical disc which rotates in a constant linear velocity as a video recording medium, and more particularly, relates to a jog method for an optical disk player so that video signals can be viewed frame-by-frame or in a slightly faster sequence during a reproducing stage.
2. Brief Description of the Related Art
Generally, a laser disk player is an electronic apparatus which records a digital signal on a disk, and thereafter, projects light having a high concentration capability such as a laser beam onto the surface of the disk and receives the reflected light, thereby reproducing the signal according to the variation of the quantity of light as the disk rotates. Here, the disk rotating methods for recording and reproducing video signals in laser disk players are classified into two types: constant angular velocity rotation and constant linear velocity rotation.
In the method for rotating the optical disk at a constant angular velocity, the number of disk revolutions per minute when the pickup for reproducing recorded video signals is located at the outermost circumference of the disk is the same as that when the pickup is located at its innermost circumference. Conventionally, the disk rotates at 1,800 revolutions per minute (rpm), by which one frame of video signals is recorded on one track of the disk according to a signal recording format of the disk. In this method, since the rotation velocities of the outer circumference and the inner circumference are constant, when performing a search jog by which images can be viewed frame-by-frame in sequence or in a slightly faster sequence, one picture can be normally reproduced with either track (outer or inner) being searched. Also, when performing a still jog for displaying one image continuously, if a track is continuously reproduced, a corresponding image is displayed as a still image.
However, in case of the method for rotating the disk at a constant angular velocity, as reproducing one side of an optical disk takes 30 minutes, accordingly it takes 60 minutes to reproduce both sides of the optical disk. Here, since only one image is recorded on a single track irrespective of the tracks of the inner and the outer circumferences during the recording of data, the recording capacity cannot be increased.
Thus, to solve the above problem, a method has been proposed to record a large amount of information on a disk, wherein signals are recorded in an equal density on the outer and the inner circumference of the optical disk, and then the recorded signals are reproduced by rotating the disk at a constant linear velocity. With the disk thus rotating, the number of revolutions per minute of the disk when the pickup is located at the outermost circumference of the disk is different from that when the pickup is located at the innermost circumference thereof. Conventionally, the disk rotates at 1,800 rpm at the innermost circumference while it rotates at 600 rpm at the outermost circumference. Thus, since the revolutions per minute at the outermost circumference is a third that at the innermost circumference, it is possible to record three-times the video signals at the outermost circumference than at the innermost circumference, in view of the recording and reproducing time. In other words, in the optical disk which rotates at a constant linear velocity, the video signals of three frames are recorded on a single track within the outermost circumference, while the video signals of one frame are recorded on one track of the innermost circumference.
To summarize the above explanation, in case of the rotation of the disk at a constant angular velocity, since the rotation velocity of the disk's outermost circumference equals that of the innermost circumference, this method facilitates the use of such functions as a search jog by which images can be viewed frame-by-frame in sequence or in a slightly faster sequence, and a still jog by which one image is continuously viewed. However, in the disk in which the rotation velocities of the outermost and the innermost circumferences are different from each other, and the video signals of three frames are recorded on a single track within the outermost circumference, while the video signals of one frame are recorded on the track of the innermost circumference, such a rotation method makes it impossible to perform the above-described functions of search jog and still jog.
That is, in the constant angular velocity mode, only one frame is recorded per track, thus, performing the jog operation is easy since all that needs to be done is to continuously reproduce the signals recorded on the track. If the pick-up is not moved from that one track, there is no way anything other than that single frame can be reproduced. On the other hand, in the constant linear velocity mode, there may be up to three frames recorded on a track, thus, it is not so easy to reproduce only a single frame. For the constant linear velocity mode, if the pick-up is merely left on one track and nothing more is done, more than one frame will be reproduced (for any track other than the innermost track) and thus the jog operation will be unsuccessful.
To enable these functions when rotating at a constant linear velocity, expensive digital memories must be used, to convert analog video signals of one frame into digital video signals, so that the digital signal can be processed by a microcomputer and converted back into the analog signal for outputting single frames or individual multiple frames.